Recently, considering environmental issues, attention has been paid to a vehicle employing a motor as a drive power source, such as an electric vehicle, a hybrid vehicle and a fuel cell vehicle. Such a vehicle includes a power storage unit implemented, for example, by a secondary battery or an electric double layer capacitor for supplying electric power to the motor, and converting kinetic energy to electric energy during regenerative braking and storing such electric power.
In such a vehicle employing the motor as the drive force source, in order to enhance acceleration performance and running performance such as travel distance, greater charge/discharge capacity of the power storage unit is desired. Here, a configuration where a plurality of power storage units are mounted has been proposed as a method of increasing the charge/discharge capacity of the power storage unit.
On the other hand, as the power storage unit stores electric energy utilizing electrochemical action, charge/discharge characteristics thereof are susceptible to a temperature. A general power storage unit is lower in the charge/discharge performance as the temperature is lower. Accordingly, in order to maintain prescribed charge/discharge performance, temperature management, in particular temperature increase control, of the power storage unit is important.
For example, Japanese Patent Laying-Open No. 11-26032 discloses a heating-up device for a battery in an electric vehicle that raises a temperature of the battery mounted on the electric vehicle. According to this device, if a detected temperature of the battery is equal to or lower than a prescribed value when an instruction is issued from at least one of unlock detection means for detecting unlock of the vehicle, timer means for notification of a set time, and input means for input of operational information, control means carries out control such that an output current of the battery greater than a current required in the battery flows.
The heating-up device disclosed in Japanese Patent Laying-Open No. 11-26032 increases battery temperature by the discharge of battery. Therefore, electric power stored in the battery is undesirably wasted. The reference above, however, does not disclose any specific method to solve such a problem.